1. Field of the Invention
The present invention relates to an image forming apparatus of which drive system for the internal components is improved.
2. Description of the Related Art
FIG. 1 shows a conventional copying apparatus as image forming apparatus. This copying apparatus scans the document using a carriage which is operated by a motor 1. The reflected light forms an image on a photosensitive drum 10 via first to third mirrors 3, 4 and 5, and a lens unit 6 and then fourth to sixth mirrors 7, 8 and 9. The surface of photosensitive drum 10 is uniformly charged by a main charger 11 and an electrostatic latent image is formed from the above-mentioned reflected image. Development of this electrostatic latent image is carried out in color or black by upper and lower developers 12 and 13 to obtain a visible image. The visible image on photosensitive drum 10 is transferred by a transfer charger 14 onto a paper fed from paper supply cassette 45 or 46. After being separated by a separation charger 15, the paper is transported to a fixing roller 17, where the image is fixed, via a transporting belt 16. After fixing, it is discharged by a exit roller 18.
By the rotation of a fan 19, the heat generated in the optical system is exhausted to the outside.
Fan 19, upper and lower developers 12 and 13, photosensitive drum 10 and fixing roller 17 are driven by double-shafted drive motor 21. That is, photosensitive drum 10 is connected to one shaft of drive motor 21 via a pulley 21a, a double-sided toothed belt 22, a pulley 23, gears 24 and 25, a pulley 26, a belt 27 and a pulley 28. Also, a developing roller 13a of lower developer 13 is connected to double-sided toothed belt 22 through a pulley 29, gears 30 and 31, and a developing roller 12a of upper developer 12 is also connected to gear 30 via gears 32, 33 and 34. Moreover, a roller 16a of transporting belt 16 is connected to double-sided toothed belt 22 via a pulley 35, gears 36, 37, 38 and 39. Furthermore, fixing roller 17 is connected to gear 38 via gears 40 and 41. Also, exit roller 18 is connected to gear 41 via gears 42, 43 and 44.
Fan 19 is connected to the other shaft of drive motor 21.
By the action of drive motor 21, fan 19 is rotated, and at the same time, double-sided toothed belt 22 is driven so that photosensitive drum 10, developing rollers 12a and 13a of developers 12 and 13, roller 16a of transporting belt 16, fixing roller 17 and exit roller 18 are respectively rotated.
However, in above-mentioned conventional copying apparatus, fan 19, developers 12 and 13, fixing roller 17 and photosensitive drum 10 have been driven by a single drive motor 21, various disadvantages have arisen because these these components could only be driven at the same speed. For example, when forming enlarged images or when color developing using upper developer 12, it is necessary to rotate photosensitive drum 10 at slow speed in order to ensure sufficient light in the former case, or from the viewpoint of the toner characteristic in the latter case. However, if this is done, fan 19 and developers 12 and 13 are also driven at slow speed. This has the disadvantages that cooling efficiency is reduced because fan 19 can not obtain sufficient air capacity. Also, developers 12 and 13 can not carry out good developing because the toner density of developing agent can not be controlled accurately.